The concept of the Kingdom is a very important biblical topic. The idea is first introduced in the Old Testament and then continues in the New Testament.
THE TERM DEFINED
The New Testament word is Basileia which is defined by W. E. Vine as:
Primarily an abstract noun denoting sovereignty, royal power dominion… then by metononmy, a concrete noun denoting the territory or people over whom a king rules.
Nat Cooper makes this point in the use of the word in the bible.
In scripture the abstract concept of the term kingdom is used the most. It is rule rather than realm. Hence, His Kingdom is His rule or reign. God’s priests and holy nation (Exodus 19:5-6; I Peter 2:5-9) became a manifestation of His sovereignty made visible in His people (Israel in the Old Testament – the church in the New Testament). 
THE KINGDOM IN THE OLD TESTAMENT
God is regarded as sitting upon a throne (Psalm 103:19a; Ezekiel 1:26-28) where he is surrounded by the heavenly host who serve Him (I Kings 22:19) and from where he watches over the whole earth (Psalm 33:13f.). In the praise offered to Him by Israel He was regarded as the King of the whole world (I Chronicles 29:11; Psalm103:19b) and of all the kingdoms of men (2 Kings 19:15; Psalm 47:2, 7). He is the eternal King (Psalm 145:13; Daniel 4:3, 4), both from everlasting (Psalm 74:12; 93:2) and to everlasting (Exodus 15:18). His right to be King rests upon the fact that He is the Creator of the heaven and the earth (Psalm 95:3-5). His kingly rule is displayed in His present jurisdiction over the nations of the world (Psalm 22:28; Jeremiah 46:18; 48:15; 51:57) and in His appointment of their rulers (Daniel 2:37; 4:17; 5:21). 
Furthermore, the Kingdom in Old Testament theology would refer to the Israelites as a nation of people. God ruled more than Israel, but had a special kingdom relationship Israel. For example, in Exodus 19:5-6 we read.
5 Now if you obey me fully and keep my covenant, then out of all nations you will be my treasured possession. Although the whole earth is mine, 6 you [a] will be for me a kingdom of priests and a holy nation.’ These are the words you are to speak to the Israelites.”
The concept of the kingdom then is not about territory but ruler ship. Unfortunately many of them did not realize that God wanted to rule the hearts of the people. No doubt this is why Jesus will sternly say to some of the Jews of his day:
The kingdom of God shall be taken away from you and given to people who will produce its fruit. (Matthew 21:43)
Each man finds something that he personally appropriates. That shows us that you can be under the dominion of God and not a member of the kingdom. Everyone in the universe is under God’s rule, because He is the Sovereign of the universe. Those who are on the earth are, in a sense, in the kingdom. But many on those on earth are not subjects of the King. 
Therefore, the way to be the true people of God is to acknowledge God’s rule. The kingdom of God must be personally appropriated. So in a sense God has always had a kingdom within a kingdom.
However, there are prophecies in the Old Testament that refer to the kingdom being established in the future, like in Daniel 2:30-45.
Daniel was summoned to interpret the vision and he said unto Nebuchadnezzar, “thou art the head of gold.” (2:38) Daniel then said, “And after thee shall arise ANOTHER KINGDOM inferior to thee; and another THIRD KINGDOM of brass, which shall bear rule over the earth.” (2:39)
After these another FOURTH KINGDOM would rise. (2:40) The first kingdom, as Daniel says, was the Babylonian kingdom. History tells us that the second world power after Babylon was the Medo-Persian kingdom. (5:28) Again, history confirms that the third world power after the Medes and Persians was the Grecian kingdom of Alexander the Great. After the Greeks came the great Roman kingdom which subdued all other kingdoms of the world. In verse 44, Daniel says, “And in the days of those kings (the Roman kings) shall the God of heaven set up a KINGDOM which shall never be destroyed, nor shall sovereignty thereof be left to another people; but it shall break in pieces and consume all these kingdoms, and IT SHALL STAND FOREVER”.
THE KINGDOM IN THE NEW TESTAMENT
It was during the days of the Roman Kings that John the Baptist said, “Repent for the kingdom of heaven is at hand.” (Matthew 3:2) It was also during the days of the Romans kings that Jesus came preaching, “The kingdom of heaven is at hand.” (Matthew 4:17; 10:7). “The time is fulfilled and the kingdom of God is at hand.” (Mark 1:15)
When Jesus declared ‘The time is fulfilled,’ he was saying that it was time for all God had said and done in Israel’s history to be brought to competition. The universal reign of God was about to be manifested in a new and special way. The hopes expressed in the Old Testament prophets were ready to be realized. 
It is clear that in several references the kingdom refers to the church. Therefore, in one sense the kingdom prophecies of the Old Testament were fulfilled when the church was established on the day of Pentecost, because after the day of Pentecost in Acts 2 the Bible speaks of the Kingdom as being in existence. (Revelation 1:9; Colossians 1:13; I Thessalonians 2:12)
The prophets closed with the promises of the Messiah’s coming. The Gospels close with the Messiah promising that the kingdom of God had just about arrived. The book of Acts (chapter 1 excepted) tells the story of a kingdom arrived.
There is a difference between the relationships designated by the terms Kingdom and Church. The kingdom refers to the relationship Christians have with God. It’s the rule or dominion of Christ in one’s heart. The church refers to the relationship Christians have with one another. These are two different terms, yet they refer to the same group of people just as father and husband are two different terms which refer to two different relationships, yet refer to the same man. These terms are not the same, they are inseparable.
These terms are applied to the same group of people but define different aspects of the body. Kingdom refers to the “governing aspect” of God’s people and church refers to them as a “called out body” of people separate from the world. The church is a monarchy with Christ as King with all authority. (Matthew 28:18; I Timothy 6:15) Only those born again, born of water and the Spirit, can enter the kingdom. (John 3:3-5) This means they must be baptized according to Christ’s will and receive the gift of the Holy Spirit. (Acts 2:38)
Matthew uses the term kingdom of heaven thirty times. Mark uses kingdom of God sixteen times. Luke uses the phrase kingdom of God thirty two times. By cross referencing parallel accounts in the synoptics, the expressions kingdom of heaven and Kingdom of God are synonymous. (Matthew 19:23; Mark 10:23; Luke 18:24) By looking at these parallel accounts it is clear that the two expressions are interchangeable. In fact in Matthew 19:23 Matthew uses the phrase kingdom of heaven, and then in verse 24 he uses the phrase kingdom of God.
Nonetheless, the idea of God wanting to rule the hearts of the people in the Old Testament is also found in the New Testament. It is still appropriate to pray, like Jesus first taught his disciples to pray, for the kingdom or the ruler ship of God to come into this world. (Matthew 6:10) However, by this I am not talking about the “millennial kingdom” but God’s reign in the hearts of men and women.
Jesus emphasized the internal aspect of His kingdom in Luke 17:20, 21.
When Jesus said (Luke 17:20, 21) that the kingdom doesn’t come with observation – that the kingdom of God is ‘within’ he wasn’t denying external things, he was emphasizing internal things. These people thought of the kingdom only in terms of victory, triumph, over enemies not knowing that the central thrust of God’s rule was to produce victory within.
In Matthew 18:3 Jesus says that one cannot enter the kingdom unless one has a child-like spirit. In Matthew 18:23 one cannot enter unless he or she has a forgiving spirit. In Matthew 25:31-46 one cannot enter it unless he or she cares for their fellowman. We should desire for God to take full control of our own personal lives. (Matthew 6:33)
THE KINGDOM IN HEAVEN
Christians have a dual citizenship. Under the flags of worldly governments we are to be citizens living exemplary lives in our communities, but there is a more valuable citizenship which is in heaven. (Philippians 3:20, 21). Those who do the will of the Father will inherit the kingdom of heaven. (Matthew 7:21) Christ now reigns in heaven. (Acts 2:30-36) Ultimately he will translate all of his subjects to the heavenly kingdom. (Matthew 25:1-13)
 W.E. Vine, Vine’s Expository Dictionary of New Testament Words (Mclean: Macdonald Publishing Company) 634.
 Nat Cooper, The Life of Christ (Lubbock: Sunset School of Preaching Extension Study Guide, 1983) 18.
 I. H. Marshal, The Zondervan Pictorial Encyclopedia of the Bible Volume Three (Grand Rapids: Zondervan publishing House, 1977) 801.
 John MacArthur, The Parables of the Kingdom (Chicago: Moody Press, 1985) 105.
 Roger Dickson, Millennial Mistake (Shreveport: Lambert Book House, Inc, 1976) 71.
 Everett Ferguson, The Church of Christ (Grand Rapids: William B. Eerdmans Publishing, 1996) 23.
 Jim McGuiggan, The Reign of God (Lubbock: Montex Publishing Company, 1979) 79.
 Wayne Kilpatrick, Church History (Florence: Heritage Christian University) 2-1.
 McGuiggan, 67.
WORSHIP IN THE EARLY CHRISTIAN CHURCH
Worship in the New Testament embraced both attitude and form. Jesus spoke of worship in this way in John 4:24:
24God is spirit, and his worshipers must worship in spirit d in truth.”
Worship must not be robbed of its emotional content or made void of feelings. However, it must also be based upon the truth of God’s word. True worship is not based upon doing things the way we like, or the way that most people like it. We have to look through scripture to find the God affirmed acts or items of praise and devotion to God.
Worship is not a spectator sport in which the worshipers sit in the stands giving their approval or disapproval to those performing in the arena. In true worship, the worshippers are involved in the action. Worship is not a dramatic production in which the ‘clergy’ are the actors and the worshippers are the audience. In true worship, God is the audience, and the worshipers are the actors.
Earle Cairns has this to say about the corporate worship of the early church.
During the first century, two services were held on the first day of the week. That day was adopted as the day of worship because it was the day on which Christ rose from the dead (Acts 20:7; I Cor. 16:2; Rev. 1:10). The morning service most likely included the reading of Scripture (Col. 3:16), exhortation…, prayers, and singing (Eph 5:19). The love feast (I Cor. 11:20-22), or agape preceded the Communion during the evening service, By the end of the first century the love feast was generally dropped and the Communion celebrated during the morning service of worship. 
It is also interesting to look at what we know about worship during the second and third Centuries.
WHERE CHRISTIANS MET
The early Christians did not think of a church as a place of worship. A church signified a body of believers who were called out of the world and into a personal relationship with Jesus Christ. They met in homes (Acts 12:12; Romans 16:5 Colossians 4:15; Philemon 1-4), the Temple (Acts 5:13), public auditoriums (Acts 19:9), and synagogue as long as they were permitted to do so (Acts 14:1, 3; 17:1; 18:4). Everett Ferguson said:
Not until the age of Constantine do we find specifically constructed buildings. Any space where an assembly was permitted was a possible site for Christian gatherings. 
Between A.D. 110 and 113 the Roman Emperor Trajan received a series of letters from Pliny, the governor of Bithynia. Pliny was concerned about what he considered a cult who met secretly within his governmental domain. His letters give some ideas about the types of things Christians practiced in their assembly in the early second century.
….It was their habit on a fixed day to assemble before daylight and recite by turns a form of words to Christ as a god; and that they bound themselves with an oath, not for any crime, but not to commit theft or robbery or adultery,
not to break their word, and not to deny a deposit when demanded. After this was done, their custom was to depart, and to meet again to take food, but ordinary and harmless food; and even this (they said) they had given up doing after the issue of my edict, by which in accordance with your commands I had my edict, by which in accordance with your commands I had forbidden the existence of clubs. 
Clement of Alexandria (150-220 A.D.)
Always giving thanks in all things to God through righteous hearing and divine reading, true inquiry, holy oblation, blessed prayer, praising, hymning, blessing, singing, such a soul is never separated from God at any time. 
THE DAY OF CHRISTIAN WORSHIP
Ignatius (born about 50 A.D.)
If therefore those who lived according to the old practices came to the new hope, no longer observing the Sabbath but living according to the Lord’s day, in which also our life arose through him and his death (which some deny), through which mystery we received faith, and on account of which we suffer in order that we may be found disciples of Jesus Christ our only teacher, how shall we be able to live apart from him for whom even the prophets were looking as their teacher since we are disciples in the spirit (Magnesians 9) 
The Epistle of Barnabus. This could be the oldest uninspired Christian writing (69-79 A.D.). He was antagonistic towards the Judaizers, and worked to harmonize the Old and New Testaments.
Moreover God says to the Jews, ‘Your new moons and Sabbaths I cannot endure.’ You see how he says, ‘The present Sabbaths are not acceptable to me, but the Sabbath which I have made in which I rested from all things, I will make the beginning of the eight day which is the beginning of another world.’ Wherefore, we (Christians) keep the eight day for joy, on which also Jesus arose from the dead and when he appeared ascended into heaven. 
THE LORD’S SUPPER
The roots of the Lord’s Supper are deeply intertwined in the Passover Meal which God instituted shortly before the Israelites escaped Egyptian bondage. Jesus did share many meals with his disciples but the Passover meal he shared with them the night he was arrested was special. (Matthew 26:17-30; Mark 14:12-26; Luke 22:1-21). Jesus gave it an all new meaning. However, our knowledge of exactly how the Lord’s Supper was celebrated in the first century is limited.
In the mid second century, sometime between A.D. 140 and 155 Justin Martyr wrote his Apology to the Emperor Antionius Pius. This philosopher, teacher, apologist informed the emperor of this account of the meal:
Having ended the prayers, we salute one another with a kiss. There is then brought to the president of the brethren bread and a cup of wine mixed with water; and he, taking them, gives praise and glory to the Father of the universe, through the name of the Son and of the Holy Spirit, and offers thanks at considerable length for our being counted worthy to receive these things at his hands. And when he has concluded the prayers and thanksgivings, all the people present express their assent by saying Amen. This word Amen is the Hebrew for ‘so be it’. And when the President has given thanks, and all the people have expressed their assent, those of us who are called deacons give to each of those present to partake of the bread and the wine mixed with water over which the thanksgiving was pronounced, and to those who are absent they carry away a portion. 
The Didache was a church manual used by the early church that some have dated between (110-120 A.D.)
Concerning the eucharist, give thanks in this way: First concerning the cup, ‘We give thanks to you, our Father, for the holy vine of David, your servant, which you made known to us through Jesus your servant. To you be the glory forever.’ Concerning the broken bread, ‘We give thanks to you, our Father, for the life and knowledge which you made known to us through Jesus your servant. To you be the glory forever. As this broken bread scattered upon the mountains and being gathered together became one loaf, so may your church be gathered together from the ends of the earth into your kingdom. Because the glory and the power are yours through Jesus Christ forever.’ No one is to eat or drink of your eucharist except those who have been baptized in the name of the Lord. 
SCRIPTURE READING IN WORSHIP
The first Christians were Jews. It should not be surprising that they would bring to their new faith and worship the custom of reading from Scripture. Paul wrote to Timothy, (I Timothy 4:13)
13Until I come, devote yourself to the public reading of Scripture, to preaching and to teaching.
Later in the second century Justin Martyr wrote,
The memoirs of the Apostles or the writings of the prophets are read as long as time permits (1st Apology67) 
The location of worship is not what is important. Worship takes place inside us. Our attitudes and emotions must blend with the God ordained items or acts of devotion. The Christians of the second and third centuries continued the external forms of worship that began in the first century by Jesus and his apostles.
We need to continue to worship God in spirit and truth today!
 Jimmy Jividen, More Than A Feeling Worship That Pleases God (Nashville: Gospel Advocate Company, 1999) 76.
 Earle E. Cairns, Christianity Through The Centuries (Grand Rapids: Zondervan, 1996) 84.
 Everett Ferguson, Early Christians Speak (Abilene: Biblical Research Press, 1981) 76.
 J. Stevenson, A New Eusebius (Southampton: The Camelot Press Ltd., 1983) 14.
 Ferguson, 82.
 Ferguson, 67
 Ferguson, 67
 J.G. Davies, The Early Christian Church (Grand Rapids: Baker Book House, 1985) 104.
 Ferguson, 93.
 Dan Dozier, Come Let Us Adore Him (Joplin: College Press Publishing Company, 1996) 196.